1. Field of the Invention
This invention relates in general to a paging system and, more particularly, to a wide area two-way paging broadcast channel with a mesh network that includes acknowledgement paging receivers integrated with each node to enable self-backhaul of the reply signal to the paging center through a paging network gateway.
2. Description of Related Art
Radio paging systems are well know and widely used. Paging systems provide the user with information from a paging party. Such information typically consists of a number for the paged party to call in response to the page. Some pagers display other information such as the time and date of the message.
One such system, U.S. Pat. No. 3,575,558, issued Apr. 20, 1971, to Leyburn, entitled "TELEPHONE PAGING SYSTEM AND METHOD", incorporated herein by reference, discloses a telephone system and radio paging system wherein a sensible signal for informing the subscriber to phone a prearranged location is activated when a paging number is dialed. The paging system is designed so that once the receiver is energized, the sensible alarm will remain activated until turned off by the possessor of the receiver. Thus, the acknowledgement paging signal is only sent once.
Other paging systems have been used which transmit limited content messages in coded form to a central station. The central station then determines the page code for the identified subscriber and transmits a signal to activate the selected subscriber's portable page receiver. U.S. Pat. No. 4,336,524, issued Jun. 22, 1982, to Levine, entitled "VIDEO DISPLAY PAGER RECEIVER WITH MEMORY", incorporated herein by reference, discloses such a system.
Still other pagers allow two-way communication between the recipient party and the paging party. U.S. Pat. No. 4,814,763, issued Mar. 21, 1989, to Nelson et al., entitled "PAGING TERMINAL APPARATUS WITH PAGE FORWARDING CAPABILITY AND METHODOLOGY THEREOF", incorporated herein by reference, discloses a paging system for automatically, or by selective response, call forwarding a message to one or more system pagers which have an acknowledge back capability.
These existing paging networks for regional wireless networking either involve public (common carrier) or private carrier networks that use licensed spectrum allocated by the Federal Communications Commission (FCC) for their exclusive use. The expense for deployment is large for acknowledgement paging networks and the cost to the end user is high ($75-100/month typically). In addition, the above type of paging networks are usually configured in a star arrangement with the transmitter at the geographic center of the network.
Additionally, the difficult task is that the above star-type networks require that the signals be routed to a central hub. To overcome these problems, intelligent wireless mesh networks have been developed for the transfer of data between a user and a remote location. Such networks provide lower network costs.
An example of a low-cost network is U.S. Pat. No. 4,939,726, issued Jul. 3, 1990, to Flammer et al., assigned to Metricom, Inc., entitled "METHOD FOR ROUTING PACKETS IN A PACKET COMMUNICATION NETWORK", incorporated herein by reference, which discloses a packet network routing method and system based on geographic coordinate identifiers. Each node in a mesh network is uniquely identified by absolute geographical coordinates or by a code indicating absolute location in an external coordinate-based reference system. The coordinates are then used as part of a packet identifier for each packet generated for use in making routing decisions.
U.S. Pat. No. 5,115,433, issued May 19, 1992, to Baran et al., assigned to Metricom, Inc., entitled "METHOD AND SYSTEM FOR ROUTING PACKETS IN A PACKET COMMUNICATION NETWORK", incorporated herein by reference, discloses a method and system for selecting which neighboring nodes to use for forwarding packets. The system bases the determination on which available node requires the least amount of power for forwarding the packet.
U.S. Pat. No. 5,079,768, issued Jan. 7, 1992, to Flammer, assigned to Metricom, Inc., entitled "METHOD FOR FREQUENCY SHARING IN FREQUENCY HOPPING COMMUNICATIONS NETWORK", incorporated herein by reference, discloses a system which can utilize the 902-928 MHz frequency band which is restricted by the FCC to a continuous transmission by a single transmitter of no more than 1 watt output power on any one channel and of no more than 400 milliseconds duration each 30 seconds. Thus, all other channels must be selected prior to retransmission on the same frequency. (See FCC Rules, Part 15.247, incorporated herein).
To meet these FCC requirements, a frequency-hopping plan may be implemented. Each receiving node establishes, in each station or node, a table of receiver frequency hopping sequence offsets of each other node within its communication range. Each node transmits an information packet that includes a hop timing offset indicator which allows the nodes to set themselves in synchronization with one another. The node checks the frequency channel to determine whether the channel is available for transmission. If the channel is not available, the node continues to monitor the selected node until an available frequency channel is found.
U.S. Pat. No. 5,130,987, issued Jul. 14, 1992, to Flammer, assigned to Metricom, Inc., entitled "METHOD FOR SYNCHRONIZING A WIDE AREA NETWORK WITHOUT GLOBAL SYNCHRONIZING", incorporated herein by reference, discloses a method for maintaining frequency and time synchronization within a mesh network. Each node collects a representation of age value for other nodes and changes slot according to a known pattern and independently of each node within the network. The slot is a frequency channel during a preselected time period. The packets are transmitted from the source node to an addressed node at a frequency and for a duration synchronous with the slot of the addressed node. Accordingly, the source node tracks the changing frequency of the receiving node.
The above mesh network concept is one ingredient of the present invention. The mesh network allows for much smaller transceiver base stations (0.5 ft.sup.3 vs. 2,000 ft.sup.3) at a lower price ($1,000.00) compared with the much higher (by orders of magnitude) typical cost of a cellular base station. Each base station is capable of providing coverage for approximately one square mile thereby substantially reducing the transmit power required in an acknowledgement pager (as low as 10 mw), enhancing battery life, and mitigating RF safety concerns. This compares to one station per 15 to 75 square miles for cellular (which requires a 0.6 w to 3.0 w cellular phone). Thus, the overall network cost of a wide area acknowledgement paging, which is well suited for use in an urban environment, is lower. In addition, wide area acknowledgement paging facilitates the use of low power user radios (acknowledgement pager) since the mesh network enables short range communications. Accordingly the mesh network transports the user traffic from the base station to a Public Switched Telephone Network (PSTN) or other network access point (e.g., a communications gateway). The combination of low cost base stations, short distance between the end user and the mesh transceiver node, and backhaul transport by the wireless mesh network rather than accessing the PSTN or other network access node (gateway) by line-of-sight microwave or leased lines, solves the battery life, safety, infrastructure cost and coverage problems discussed above.
Although the wireless mesh network approach is an improvement over prior methods of communicating information over a wireless network, it carries its own drawback. For instance, even though wireless mesh networks are the right answer for low-cost geographic coverage and self-backhaul to a network gateway, they still present a further barrier to subscriber equipment. That is, the cost of said equipment remains prohibitively high.
For example, the cost of subscriber equipment is still comparable to the base station cost since the base station is a peer to the subscriber unit. The estimated cost of $500 for the subscriber unit is still too high for most potential users. However, consumers expect low-cost connectivity. Paging is a good example of such a service. For $9 to $45/month, broadcast paging is available at a price consumers can afford with a device that costs them $80 to $180.
In addition, the network equipment described in U.S. Pat. No. 5,079,768 requires a radio that uses a frequency synthesizer for spread spectrum, and transmits roughly 3 watts of power (marginally acceptable from a user's safety standpoint). A radio with this much transmit power, lacking the wake-sleep efficiency of a paging receiver, and the complexity of a frequency synthesizer, will not work long on a set of batteries and will be prohibitively inconvenient and expensive.
Thus, there is a need for wide area two-way paging using a mesh network with paging receivers installed and integrated with mesh node base stations.